Polymeric materials are used in an almost limitless variety of applications. For instance, thermoplastic polymers are used to form films, fibers, filaments, and may also be molded or extruded into various useful articles. For example, polymeric materials are commonly used to form various containers, thereby replacing conventionally used glass materials.
As opposed to glass materials, however, some polymeric materials have inferior gas barrier properties in comparison to glass. For example, although polyesters, such as polyethylene terephthalate (PET), are widely used in constructing bottles and containers which are used for carbonated beverages, fruit juices, and certain foods, the polyesters unfortunately have limited barrier properties with regard to oxygen, carbon dioxide and the like. As such, in the past, these materials have been used sparingly in applications where relatively high gas barrier properties are needed. For instance, polyester containers are not always well suited for products requiring a long shelf life. Polyester bottles may also cause food products, such as beer and wine, to spoil due to oxygen permeability. Due to these shortcomings, those skilled in the art have attempted to improve the gas barrier properties of polymers.
For example, in the past, organically treated natural clays have been incorporated into polymers, such as polyesters, in order to improve the barrier properties of the materials. If well dispersed within the polymer, the clay particles diminish the permeability of gases through the polymer by making the path for gas diffusion more tortuous. The barrier enhancement generally depends upon the aspect ratio of the particles and the degree of exfoliation of the particles in the polymer.
One challenge has been to maximize the exfoliation of the clay into the polymeric material. In order to maximize exfoliation, in the past, clays such as montmorillonite, prior to being combined with a polymer were first ground or pulverized to a very small size. In many applications, impurities such as quartz were then removed from the clay particles. After being ground or pulverized, the clay materials exist as a fine powder. For example, the clay materials may comprise relatively large agglomerations that contain many layers of individual platelets that are closely stacked together. During exfoliation, the object is to break as many layers apart so as to form single layer particles or particles that have only a few layers, which are referred to as tactoids.
In order to separate the layers so that the clay material becomes exfoliated into a polymer, in the past, the clay material has been combined with various organic cations, such as ammonium ions. Examples of polymer/clay composite materials as described above are disclosed, for instance, in U.S. Pat. Nos. 6,034,163; 6,071,988; 6,084,019; 6,162,857; 6,337,046; 6,359,052; 6,384,112; 6,395,386; 6,417,262; 6,486,252; 6,486,253; 6,486,254; 6,548,587; 6,552,113; 6,586,500; 6,653,388; and 6,737,464, which are all incorporated herein by reference.
Although the above body of work represents great improvements and advancements in the art of forming polymer composite materials having improved barrier properties, further improvements still remain. In particular, a need exists for a material capable of improving the gas barrier properties of polymer that may more easily be exfoliated into the polymer. A need also exists for a particle that may be exfoliated into polymers that does not contain substantial amounts of impurities. A need further exists for a particle that can be exfoliated into polymers in relatively great amounts when necessary for various applications. A need further exists for an improved process for exfoliating particles into a polymeric material.